JPH0399777A - Arc welding power unit - Google Patents

Abstract

PURPOSE:To increase the decreasing speed of an electric current as much as possible by providing a DC/DC converter circuit to regenerate charging energy of a capacitor connected to a secondary winding of a DC reactor on a DC power source. CONSTITUTION:The arc welding power unit is provided with the DC/DC converter circuit 14 to convert the output of the DC power source into desired arc welding electric power by using a switching element 12. Electromagnetic energy accumulated in a DC inductance of an output circuit is once absorbed in the capacitor 13 and then, regenerated on the DC power source side when an output current command is reduced. When an output current is to fall, the electromagnetic energy accumulated in the DC reactor 10 before that is transferred forcibly to others. The rise of the current can be speeded up while maintaining the specified number of rises of the current suited for arc welding without using a high-speed element and a high-capacity element, especially. By this method, the generation of spatters can be reduced and further, arc stability is maintained and electric power efficiency can be also improved.

Description

[Detailed Description of the Invention] <Industrial Application Field> The present invention relates to an arc welding power supply device that adjusts the output of a DC power supply intermittently using a switching element and supplies it to an arc load. The present invention relates to a power supply device suitable for pulsed arc welding in which a high current is periodically supplied to a welding part, and short-circuit transfer type arc welding in which short circuits and arc generation are repeated.

<Prior Art> In an arc welding power supply device for the purpose mentioned above, it is necessary to control the output current at high speed in order to further improve welding performance. To achieve this purpose, DC power supplies have recently been controlled ON-OFF using switching elements.
- It has been proposed to first convert the AC into high-frequency AC and then rectify it via a transformer, or perform chopper control using high-speed switching.

FIG. 6 is a connection diagram showing an example of a conventional forward converter type device, which is one of these types.

In the same figure, reference numeral 101 is a DC power supply, which usually rectifies a commercial AC power supply and smoothes it by connecting a capacitor in parallel to the DC output side. 102a and 1021) are switching transistors connected in series with the primary winding 103p of the transformer, and 104a and 104b are connected to each series circuit of the switching transistor 102a or 102b and the primary winding 103p of the transformer. These are diodes connected in parallel, and their polarity is determined by each transistor 1 as shown in the diagram.
The polarity is set to be opposite to the conduction direction of 02a and 102b. 103 is a transformer, and the above-mentioned primary winding 103
It has a p-type winding and a secondary winding 103s, and has characteristics suitable for the ON-OFF frequency of the transistors 102a and 102b. 105 is an output rectifying diode, 1
06 is a freewheeling diode for sustaining and smoothing the output current when the transistors 102a and 102b are turned off, and 107 is a DC reactor that constitutes an output smoothing circuit together with the freewheeling diode 106.

108 is a consumable electrode fed by a feeding mechanism (not shown), 109 is an object to be welded, and 110 is a welding arc. Further, 111 is a reference signal setting circuit that outputs a reference signal Ir of the output current, and 112 is an output Ir of the reference signal setting circuit 111 and an output 1a of the welding current detection circuit 113.
This is a control circuit for controlling the transistors 102a and 102b ON-OFF at a predetermined frequency with a time width determined by a difference signal to obtain a desired output, and a known PWM (pulse width) modulation circuit is used. Ru.

In the device shown in the figure, when a pulse train of a predetermined duty is supplied from the control circuit 113 to the transistors LOZa and 102b, each transistor becomes conductive each time, and current flows from the DC power supply 101 to the primary winding 103p of the transformer 103. . The polarity of the primary and secondary windings of the transformer 103 is shown in the diagram.
If the current flows through the primary winding 103p, the diode 105, the DC reactor 107, the electrode 108, the object to be welded 109, and the secondary winding 10 of the transformer 103 are
As the current flows through the 3s path and gradually increases, electromagnetic energy is stored in the reactor 107.

When the transistors 102a and 102b are cut off, the electromagnetic energy stored in the accelerator 107 passes through the free-wheeling diode 1.08 to the electrode 108 and the workpiece 10.
9 and the welding current continues. At this time, transformer 1
In the primary winding 103p of No. 03, a current that attenuates in the same direction as the previous one flows through a diode 104a.

DC power supply 101, diode 104b, primary winding 10
3p and resets the magnetic flux generated in the iron core of the transformer 103 during the previous transistor conduction period. The conventional device shown in FIG. 6 which operates in this manner has a transistor 102.
a, 102b, transformer 103. Diode 104a.

A DC/DO conversion circuit composed of forward converters 104b, 105, and 108,
By increasing the operating frequency of the transistor, the output is controlled finely and at high speed.

<Problems to be Solved by the Invention> When the above-mentioned conventional device is used for arc welding using a consumable electrode, there are the following problems.

That is, when the reference signal 1r is changed to a low value in order to shift from a high current output state to a low current output state, Ia>Ir and the transistors 102a and 102b are completely cut off. Due to the electromagnetic energy previously stored in the reactor 107, the output current ra continues to flow through the free-wheeling diode 106 with approximately the same value as the original current value.

The inductance of this current beam acdle 107 and the electrode 1
08, the arc 110, and the arc load consisting of the workpiece 109. In order to increase the speed of change in the output current, it is necessary to shorten the fall time of this current, and for this purpose, the inductance of the DC reactor 107 must be reduced. However, if the inductance of the DC reactor is reduced, the time constant for smoothing the output will also be shortened, so in order to obtain a smooth output, the operating frequency of the DC/DC conversion circuit must be set high. Switching loss increases, leading to a decrease in efficiency, and it becomes necessary to prepare transistors for high-speed switching, resulting in high costs. Furthermore, if the inductance of the reactor 107 is reduced, the rate of increase in output current when a load short circuit occurs increases, making overcurrent protection difficult and requiring the use of large-capacity elements.

Furthermore, in arc welding using a consumable electrode, the electrode and the workpiece may be short-circuited at the start of welding and during welding. At this time, the short-circuited portion is heated and melted by the output current from the power source, and is narrowed by the pinch force caused by the supplied current, and finally the short-circuited portion breaks and transitions to an arc. This short-circuit phenomenon occurs frequently in pulsed arc welding using a consumable electrode and supplying high and low currents alternately, and especially during high-speed welding, undercuts and humping beads occur. This occurs frequently when performing a welding method called short-circuit transfer type pulsed arc welding, which uses a relatively low welding voltage and welding current to prevent such welding defects.

In this short-circuit transfer type arc welding method, a droplet gradually grows at the tip of the consumable electrode during arc generation, and this eventually contacts and short-circuits the object to be welded. At this time, most of the droplets are transferred to the workpiece due to the surface tension of the molten metal, but the remaining droplets are strongly squeezed by the pinch effect of the welding current, cutting the short circuit and regenerating the arc. The process is repeated. When using a pulsed arc welding power source that alternately supplies high current and low current for such short-circuit transition type arc welding, the consumable electrode and the welded object are melted mainly by the arc generated during high current. Welding conditions are often selected so that the current is switched to a low current when the droplets have grown sufficiently to cause a short circuit to the workpiece.

The short circuit that occurs in this way is broken by the transfer due to the surface tension of the droplet and the pinch force of the welding current, and the arc is regenerated. However, if a large current flows between this short circuit and the arc regeneration, the short circuit occurs. The molten metal is blown away and becomes spatter.

On the other hand, the high current period can be changed arbitrarily by setting the duration of the reference signal Ip.
The gradual decrease time from the high current to the low current period after switching from Ib to Ib depends on the inductance of the output circuit and is unique to the device, which cannot be adjusted by setting. Therefore, short circuit transition type pulsed arc welding is also required to shorten this current decay time.

Means for Solving the Problems> The present invention provides an arc welding power supply device having a DC/DC conversion circuit that converts the output of a DC power supply into desired arc welding power using a switching element. The electromagnetic energy accumulated in the inductance is once absorbed into the capacitor when the output current command decreases, and then regenerated to the DC power supply side, thereby making the rate of current decrease as fast as possible.

Function> In the present invention, when the output current should fall, the electromagnetic energy previously stored in the DC reactor is forcibly transferred to another, so it is not necessary to use a particularly high-speed element or a large-capacity element. Since the current can rapidly fall while maintaining the current rise time constant suitable for arc welding, the generation of spatter can be reduced as much as possible.

<Embodiment> FIG. 1 is a connection diagram showing an example when the present invention is applied to a DC/DC conversion circuit using a two-stone forward converter. In the figure, 1 is an AC power source, which is usually a three-phase or single-phase commercial AC power source. 2 is AC power source 1
This is a rectifier circuit that rectifies the AC power to obtain DC power, and a known circuit system compatible with the AC power source 1 is used. Reference numeral 3 denotes a capacitor for smoothing the output of the rectifier circuit 2 and for storing electric power regenerated by the operation of the present invention described later, and can be omitted when included in the rectifier circuit 2. This AC power source 1, rectifier circuit 2, and capacitor 3 constitute a DC power source. As this DC power source, in addition to the one shown in the drawings, a power source such as a DC generator or a storage battery can be used. 4a, 4b are switching transistors, 5a,
5b is a diode, and 7 is a transformer, which has a primary winding 7p and a secondary winding 7s. Here, the diode 5a is connected in parallel to the series circuit of the transistor 4a and the primary winding 7p with opposite polarity as shown in the figure, and the diode 5b is similarly connected in parallel to the series circuit of the transistor 4b and the primary winding 7p. connected, transistors 4a, 4b, diode 5
A, 5b, and transformer 7 constitute a forward converter, and its operation is similar to that of the conventional device shown in FIG. 6 a s6b is a reverse voltage protection diode for the transistors 4a and 4b; 8 is a diode for rectifying the output of the secondary winding 7S of the transformer 7; 9 is a diode for the transistors 4a and 4b;
This is a free wheel diode (flywheel diode) for releasing the energy stored in the DC reactor IO and sustaining the output current during the period when b is OFF. 1
0 is a DC reactor, which together with a diode 9 forming a freewheeling circuit forms an output current smoothing circuit.

11 is a secondary winding magnetically coupled to the DC reactor 10, 12 is a unidirectional switching element such as Cyrisk, and 13 is a capacitor connected to the secondary winding 11 in series with the switching element 12. be. 14 is a 1 DC/DC converter for boosting the terminal voltage of the capacitor 13 and regenerating it into a DC power supply. 15 is a reverse blocking diode provided on the output side of the DC/DC converter.

16 is a welding current (output current) detector using a current shunt or a DC transformer, and outputs a voltage corresponding to the welding current Ia. 17 is a reference signal setting circuit for setting the welding current, and 18 is a comparator, which compares the output Sl of the reference signal setting circuit 17 and the output s2 of the output current detector 1G, and generates an error signal Δv(-sl-sz). Output. 19 inputs the error signal Δ■ and generates a drive signal S with a pulse width according to the input signal.
This is a PWM modulation circuit that outputs a signal S3, and the transistors 4a and 4b are ON-OFF controlled by this signal S3. A comparator 20 compares the error signal Δ■ with the ground potential and outputs a high level signal during a period when Δv<O, and detects a period in which the output current is excessive and should fall. This comparator 20
The output of is supplied to the switching element 12 to make it conductive. 21 is a consumable electrode that is automatically fed by a feeding mechanism (not shown), 22 is an object to be welded, and 23 is a welding arc.

The operation of the embodiment shown in FIG. 1 will be explained with reference to the diagram in FIG. 2. In FIG. 2, (a) represents the reference signal S1, (
b) is the output current 1a, that is, the output S2 of the detector 16, (C)
is the error signal Δ■, (d) is the output s4 of the comparator 20, (e
) indicate the output s3 of the PWM modulation circuit 19, respectively. As shown in FIG. 2(a), the reference signal S1 is at time t=
If tl is changed from a low value of 11 to a high value of Ih, the value ΔV will be small because it was in an equilibrium state until then.
The error signal ΔV which was O is Δv LrI h I
J! As a result, the PWM modulation circuit 19 outputs a drive signal s3 with a pulse width close to the maximum width, and thereby the transistor 4a.

The conduction time rate of 4b increases rapidly, and the average value of the output voltage of transformer 7 increases. Due to this rapid increase in output voltage, the output current gradually increases according to the time constants of the output circuits such as the DC reactor 10 and the arc load. At this time, the comparator 20 detects that the human input signal Δ■ is positive (Δv>0) because sl > sz, so the output signal S4 remains at a low level, so the switching element 12 is in the cutoff state, and the DC reactor 10 exhibits the same reactance as if its secondary winding were not present. As the output current increases, the error signal ΔV decreases, and when it reaches Io cape Ir, the error signal ΔV becomes P
A small positive value ΔVO determined by the amplification factor of the feedback circuit including the WM modulation circuit 19 is reached, resulting in an equilibrium state. Next, at time t=t2, when the reference signal sl returns from ■1 to Ih, the error signal ΔV""5l-82 becomes negative,
As a result, the output pulse width of the PWM modulation circuit 19 becomes zero, and the transistors 4a and 4b are kept completely cut off.

As a result, the output voltage of the transformer 7 becomes zero, but during the period t1
The current continues to flow through the diode 9 due to the electromagnetic energy stored in the DC reactor 10 between t2 and t2. However, since the error signal Δ■ is negative at this time, the comparator 20 outputs a high level signal, causing the switching element 12 to conduct. In addition, in the secondary winding 11 connected to the reactor 10, since the current ■0 changes in the direction of decreasing, a voltage is generated in the direction that prevents this. If the determination is made as shown in the symbol, when the switching element with the polarity shown in the figure becomes conductive, the energy stored in the reactor 10 is transferred to the secondary winding 1 through magnetic coupling, and this is stored in the capacitor C1. It will be done. Therefore, the energy stored in the reactor 10 is rapidly transferred to the capacitor C1, and as a result, the current Io flowing through the welding circuit is rapidly reduced.

Output current Io decreases and Io hesitates I J! Then,
sl→s2, the error signal ΔV≧0, and equilibrium is established. At this time, the signal s4 becomes low level, and the switching element 12 is reverse biased by the charging voltage of the capacitor CI and is cut off. On the other hand, the energy charged in capacitor CI is boosted by DC/DC converter 14 and capacitor 3. That is, it is regenerated into a DC power source.

Note that the charging energy of the capacitor CI may be discharged through a resistor etc. after the output current has decreased and stabilized, but it is better to regenerate it to the DC power supply as in the above embodiment, since power efficiency can be increased. It's advantageous.

FIG. 3 shows an embodiment in which the present invention is applied to a pulsed arc welding power supply device that alternately supplies high current and low current. In the figure, numerals 1 to 23 indicate the same functions as those in the embodiment shown in FIG. Among these, the DC reactor 10 and the secondary winding II constitute an autotransformer, and are constituted by a part of a common winding 24. 25 is a first reference signal setting circuit for setting the welding current when the current is low, 26 is a second reference signal setting circuit for setting the welding current when the current is high, and 27 is a circuit for setting the welding current when the current is high. An oscillation circuit 28 generates a sawtooth wave or a triangular wave sp for setting the repetition frequency of the oscillation circuit, and 28 is a time ratio setting circuit for determining the ratio between the high current period and the low current period, and outputs a DC voltage vp. 29 is a comparator, which compares the output sp of the oscillation circuit 27 and the output vp of the time ratio setting circuit 28, and a period of sp<vp is a high current period T.
A high level signal is output as p, and a low level signal is output during the remaining period as low current period Tb. The oscillation circuit 27, time ratio setting circuit 28, and comparator 29 are pulse width control circuits, and constitute a time setting circuit for determining high and low current periods. Of course, this time setting circuit may be one in which the pulse width of a multivibrator is made variable in addition to the one shown in the figure. 30 is each output signal Ib of the first and second reference signal setting circuits 25 and 26.

It is a signal synthesis circuit that receives Ip and the output signal of the comparator 29 as input, and outputs Ib during the period Tb and Ip during the period Tp. For example, when the output signal of the comparator 29 is high level, the signal 1p is output ( When the output signal of the comparator 29 is at low level (Tp), the analog switch conducts the signal 1b.
It can be configured by an analog switch that is made conductive at time b) and an adder that adds the outputs of both analog switches to produce an output signal sl.

The operation of the embodiment of FIG. 3 will be explained with reference to the diagram of FIG. 4. As shown in FIGS. 4(a) and 4(b), depending on the set value vp of the time comparison setting circuit 28, during the period when vp>sp, the output of the comparator 29 becomes a high level signal (Tp off period, and vp
The period <sp becomes a low level signal (Tb period). Based on the output of the comparator 29, the signal synthesis circuit 30 switches the input signal Ip or Ib and supplies it to the comparator 18 as a reference signal s1.

The comparator 18 compares this input signal s1 with the output signal s2 of the output current detector 16, obtains a difference signal Δv−s1s2, and outputs P
The signal is supplied to the WM modulation circuit 19, and the PWM modulation circuit 19 outputs a conduction drive signal s3 having a pulse width corresponding to this error signal, as shown in FIG. 4(g), thereby rendering the transistors 4a and 4b conductive. As a result, the output current Io changes to a value corresponding to the reference signals Ip and Ib, as shown in FIG. 4(d).

At this time, since the switching element connected to the secondary winding 11 of the reactor 10 remains cut off, the rise of the output current Io increases with the same time constant as when the DC reactor 10 does not have a secondary winding. On the other hand, when the welding current falls, when the output signal s1 of the signal synthesis circuit changes from Ip to a low value Ib, the error signal Δv=sl - s2 <Q and the output signal of the comparison circuit 20 becomes high level, which causes the switching Element 12 becomes conductive. As a result, Tp
During this period, the electromagnetic energy stored in the DC reactor 10 is transferred to the capacitor 13 via the secondary winding having an autotransformer structure. As a result, the output current to the welding circuit rapidly decreases, and when it reaches I o ''F I b, ΔV≧0 and balance is achieved.

FIG. 5 shows another embodiment of the invention. The device shown in the figure shows an example in which the present invention is applied to a chopper type series regulator type power supply device using series transistors, and a series transistor 31 is used instead of the forward converter type shown in Figs. 1 and 3. It is a provision. Further, as a switching element connected to the output circuit of the secondary winding 11 of the DC reactor 10, a self-extinguishing switching element consisting of a transistor 33 and a reverse blocking diode 35 is used. Note that 32 and 35 are diodes connected in antiparallel for protection of each switching transistor. Other elements having the same functions as those of the embodiment shown in FIGS. 1 and 3 are given the same reference numerals.

In the device shown in the figure, the output S2 of the output current detector 16 is compared with the reference signal setting circuit s1 by the comparator IB, and the error signal ΔV is supplied to the PWM modulation circuit 19 to determine the conduction time rate of the switching transistor 31. be done. This error signal ΔV is also supplied to the comparator 20, and a low level signal Δv is supplied to the transistor 33 while Δv>Q, and a high level signal is supplied to the transistor 33 while Δv is 0. Therefore, when the setting value of the reference signal setting circuit 17 is constant or when the arc 23
When is occurring normally, ΔV≧0, so the transistor 33 does not conduct, and the output current flows through the DC reactor 1.
0 varies according to the same time constant as when no secondary winding is provided. On the other hand, when the set value of the reference signal setting circuit 17 suddenly decreases, or when the electrode 21 and the workpiece 22 are short-circuited and the load suddenly decreases, s2 >sl transiently, and the error signal Δv<Q. At this time, the PWM modulation circuit has an excessive output current, so the switching transistor 3
The conduction time rate of transistor 1 is set to zero, and comparator 20 supplies a high level signal to transistor 33 to make it conductive.

As a result, the electromagnetic energy stored in the DC reactor 10 is transferred to the capacitor 13 via the secondary winding 11 due to magnetic coupling, whereby the output current Io rapidly decreases. Output type 0 When the current becomes 81≧82 due to a decrease, the transistor 33 is cut off again, and the time constant of the change in output current returns to the original value.

In addition to the above embodiments, the present invention converts the output of a DC power supply into high-frequency AC using a bridge type or push-pull type inverter, converts the voltage appropriately using a transformer, and rectifies the output of the transformer. Of course, the present invention can also be applied to an arc welding power source that obtains DC output.

<Effects of the Invention> Since the device of the present invention operates as described above, it is possible to increase the rate of decrease in output current without reducing the inductance of the DC reactor. As a result, not only can the generation of spatter be reduced and the stability of the arc can be ensured, but the device can also be made simple and inexpensive, and power efficiency can also be improved, among other effects.

[Brief explanation of drawings]

Fig. 1 is a connection diagram showing an embodiment of the present invention, Fig. 2 is a diagram for explaining the operation of the device in the embodiment of Fig. 1, and Fig. 3 is a connection diagram showing another embodiment of the invention. 4 is a diagram for explaining the embodiment of FIG. 3, FIG. 5 is a connection diagram showing yet another embodiment of the present invention, and FIG. 6 is a connection diagram showing an example of a conventional device. It is. 1... AC power supply, 2... Rectifier circuit, 3...
... Capacitor, 4a, 4b, 31... Switching transistor,
5a, 5b, [ia, 6b, 8. 9.15
．． 32.34 35...Diode, 10...DC reactor, 11...Secondary winding,
12... Switching element, 13... Capacitor, 14... DC/DC converter, 16... Output current detector, 17... Reference signal setting circuit, 18.2
0... Comparison circuit, I9... PWM modulation circuit

Claims (1)

[Claims] 1. In an arc welding power supply device in which the output of a DC power source is adjusted intermittently by a series switching element,
a DC reactor connected in series between the switching element and the load; and a DC reactor magnetically coupled to the DC reactor.
A series circuit consisting of a secondary winding, a capacitor connected to the secondary winding, and a switching element that becomes conductive when the output current falls, and a DC/DC conversion circuit that regenerates the charging energy of the capacitor to the DC power supply. An arc welding power supply device equipped with. 2. The arc welding power supply device according to claim 1, wherein the secondary winding of the DC reactor is a winding insulated from the primary winding. 3. The arc welding power supply device according to claim 1, wherein the secondary winding of the DC reactor constitutes an autotransformer that shares part or all of the winding with the primary winding.